The neurohypophysial hormone, oxytocin, is known for its critical role in female reproductive physiology, such as uterine contraction during labor and milk ejection while nursing. Oxytocin is also released in the brain and modulates many aspects of social behaviors, including social recognition, maternal behavior and pair bonding. Oxytocin influences social behaviors by binding to the oxytocin receptor (OXTR) located in various parts of the brain. In recent years, the oxytocin system in the brain has received tremendous attention as a potential pharmacological target for the treatment of many psychiatric disorders, such as anxiety, autism spectrum disorders, and postpartum depression. Despite the importance, the cellular characterization, connectivity, and regulation of OXTR expressing neurons in the brain is still largely unknown. We recently discovered a group of estrogen-dependent OXTR neurons that is exclusively present in the anteroventral periventricular nucleus (AVPV) in females, but not in males. The overall long-term objective of our project is to elucidate the behavioral significance and regulatory mechanisms of OXTR neurons in the AVPV. Because the AVPV is known to regulate parental behavior in a sex-specific manner, we hypothesize that oxytocin exerts parental behavior via OXTR neurons in the AVPV. To address this hypothesis, we will employ a Designer Receptors Exclusively Activate by Designer Drug (DREADD)-based approach to specifically manipulate activity of OXTR neurons in the AVPV in vivo and in vitro. DREADDs are mutated G-protein coupled receptors that are exclusively activated by the pharmacologically inert ligand clozapine-N-oxide (CNO) at nanomolar potency. Both the stimulatory and inhibitory DREADD will be introduced specifically to OXTR neurons using Cre-recombinase-dependent viral vectors. Neural activity of the DREADD-expressing OXTR neurons will be manipulated by CNO. In Aim 1, the effect of inhibition/activation of OXTR neurons in the AVPV on maternal behavior will be examined. In Aim 2, anatomical and functional connectivity of OXTR neurons in the AVPV will be examined using the Channelrhodopsin-assisted circuit mapping (CRACM) technique combined with electrophysiology and Ca++ imaging. The proposed studies will elucidate the sex-specific oxytocin neural circuitry system that regulates sex- specific social behaviors. The findings from this project will provide useful insight into sex-specific pharmacological interventions that may likely treat sex typical psychiatric disorders, such as postpartum depression (PPD).